Weird Engine Concerns (2F) (1 Viewer)

[stuxtruth]

So to make a long story short, I was out driving my 74 FJ40 and stopped to run into Home Depot. Upon coming out of the store and starting the car, a big blue puff of smoke came out. I’ve noticed that it will do this only when the engine is hot and sits for a few minutes. No smoke at cold startup.

So I come home and decide to do a compression test. My readings are roughly 150, 150, 90, 150, 150, 150. This was a dry test, hot engine, WOT. So I decide to go ahead and do a wet test to see if it’s the rings. I get the same exact results as the dry test so I’m thinking maybe it has something to do with the valve train.

Fast forward 24 hours and I pull the valve cover off and check my valve clearances they check out to FSM spec. I’m sitting here and have all the plugs out so I figure I might as well do another compression test just out of curiosity and I get 150 psi on the cylinder that was 90 psi when it was hot! What gives??

I go ahead and order a new valve cover gasket and valve stem seals. I go ahead and do a leak-down test on the engine and all six cylinders are showing good results (less than 20% leakage with a cold engine). There is no air escaping through the intake, exhaust or radiator. Just a very small about through the dipstick tube (pretty sure this is normal).

By the way, the engine runs good.

Can you guys give your opinions on what the heck you think is going on to cause this blue smoke?

 

[Steamer]

Black smoke = fuel.
White smoke (steam) = water (coolant)
Blue smoke = oil.
Bad valve seals usually show themselves with blue smoke most often on first start up or when starting off after sitting for a traffic light.

There was some info on changing valve seals discussed here just the other day. "Click Here"

 

[pb4ugo]

I would probably do another hot compression test in the future to confirm your numbers. 1st, I'd also do a cyldr leak down test on the cyldr in question when hot. Bad valve seals shouldn't effect compression numbers. You could have a sticky or slightly bent valve that shows itself when hot or a weak valve spring. Could be a bad valve guide. Metal expands when hot. It seems a valve is not sealing correctly when hot.

 

[1911]

Blue smoke on startup only is the classic sign of worn valve guide seals. When you shut the engine down, oil that was circulating through the rockers drips down through the worn valve guide seals into the combustion chamber. When it's running, the small amount of oil just burns off unnoticed (except for maybe oil consumption), but when it sits not running then enough oil pools in the combustion chamber to make the noticeable cloud of smoke on startup.

 

[stuxtruth]

Thanks for the info guys. I went ahead and grabbed everything necessary to do the valve stem seals. I'm going to get it all buttoned back up and do another hot engine compression test. I'll let you guys know how it turns out.